Transceiver technology has and continues to develop at a rapid pace with concomitant challenges for designers. For instance, one area of development in particular is the use of increased carrier frequencies for various RF protocols. As carrier frequencies increase, the fidelity (e.g., the goodness or reliability) requirements for RF front-end components (e.g., pre-baseband on receive side and post-baseband on transmit side) become more critical. Another area of development that presents challenges to designers is the miniaturization of circuit components. As circuits and circuit components are scaled down in size, larger variability in performance is created due to manufacturing process variations. In the nanometer design regime, analog and RF circuits are expected to be increasingly more susceptible to process, noise and thermal variations than ever before.
Process variations such as the shift of threshold voltage, oxide thickness, and geometric size of a transistor directly affect the circuit performance. Shifting threshold voltages on n-channel metal oxide semiconductor (NMOS) and p-channel MOS (PMOS) devices of a mixer, low noise amplifier (LNA), or power amplifier, for example, can affect the performance specifications of these circuits, such as gain. Thermal variations affect carrier mobilities of NMOS and PMOS devices differently, further affecting circuit performance. For example, threshold voltage shift affects the transistor bias point and hence, its transconductance. Similarly, as temperature changes, NMOS and PMOS transistors have a threshold voltage shift VT in magnitude of roughly 2 mV/K. The coefficient for most NMOS transistors has a negative sign and the PMOS transistor coefficient has a positive sign. These threshold voltage shifts can be very detrimental to the overall circuit operation. Also, the drift of the bias voltage reference and current sources can force the transistors into the wrong region of operation and drastically reduce the overall performance. In addition, carrier electron mobility inside the transistor is a function of temperature (e.g., mobility is proportional to temperature raised to the −1.5 power). Thus, circuits that are operating at high temperatures can experience severe carrier mobility degradation and drastically reduced NMOS drain-to-source currents. This results in reduced transconductance, and significantly shifts input and output impedance of the transistors. Carefully constructed RF matching circuits generally work poorly when the transistor input and output impedances shift due to high temperature.
To ensure the fidelity of the various components of a device, manufacturers test the device and/or components using external test equipment for various specifications before shipment. Most specifications pertain to performance parameters such as gain, noise, and/or the measure of non-linearity of the components. External testing equipment is typically designed to measure the performance at a predetermined range of device operating conditions, often without the ability to scale to higher-than expected test frequencies. In the absence of scalability, the manufacturer often needs to invest in new automatic test equipment (ATE) worth millions of dollars, while the existing ATE systems become obsolete.
One solution to the above-mentioned problems is to provide only some of the functionality in the ATE. In addition, load boards comprising an electronic board with selective external test equipment functionality corresponding to specification tests deemed most critical to the fidelity of the component to be tested may be used during production testing.
Other solutions include on-chip systems. The on-chip systems employed to date present many design challenges. For instance, for on-chip solutions, if the test circuitry is too complex, there is a risk that reliability of the entire part may be compromised. Further, yield of the die may be compromised if the additional circuitry consumes too much area on the chip. Another cause of concern is the effect of process variations on the performance of RF circuits resulting in loss of manufacturing yield. In addition, such circuits have to function reliably under adverse field conditions (thermal, noise and battery power conditions).